LeetCode:Surrounded Regions（回溯法）

 

Given a 2D board containing 'X' and 'O', capture all regions surrounded by 'X'.

A region is captured by flipping all 'O's into 'X's in that surrounded region.

For example,

X X X X
X O O X
X X O X
X O X X

After running your function, the board should be:

X X X X
X X X X
X X X X
X O X X

class Solution {
public:
    void solve(vector<vector<char>>& board) {
        int m=board.size();
        int n=board[0].size();
        //先对边上的节点DFS
        for(int i=0;i<m;++i)
            for(int j=0;j<n;++j)
            {   
                //把边边的映射成为1
                if(i==0||j==0|i==m-1||j==n-1&&board[i][j]=='0')
                    DFS(board,i,j,'1');
                else
                    continue;
            }
            
       //再把剩下的0联通的映射成为x
       
       for(int i=0;i<m;++i)
        for(int j=0;j<n;++j)
            if(board[i][j]=='0')
                DFS(board,i,j,'x');
        
        //再把1的反转为x
        for(int i=0;i<m;++i)
            for(int j=0;j<n;++j)
                if(board[i][j]=='1')
                    board[i][j]=='0';        
    }
    
    void DFS(vector<vector<char>> &board,int x,int y,char c)
    {
        if(x<0||y<0||x>=board.size()||y>=board[0].size())
            return;
        
        //把所有的都映射成为1
        if(board[x][y]=='0')
        {
            board[x][y]=c;
            DFS(board,x-1,y);
            DFS(board,x+1,y);
            DFS(board,x,y-1);
            DFS(board,x,y+1);
        }
        
    }
};